WASHINGTON (USA TODAY) -- Washington's latest political scandal involves a little-known unit of the Internal Revenue Service that determines which groups don't have to pay taxes. Staff in that unit had singled out conservative political groups for greater scrutiny of their applications for tax-exempt status, an IRS official said last week. President Obama said Monday the IRS must not be "anything less than neutral in terms of how they operate ... I have no patience for it. I will not tolerate it."

The IRS inspector general is likely to report this week on what the agency was doing, but here is what we know:

Q: What exactly has the IRS apologized for?

A: The IRS says it subjected Tea Party-affiliated groups to additional scrutiny based solely on the name and stated goals of the organization. Often, those groups were asked invasive questions about their donor lists, affiliations and contacts with the media - questions not routinely asked of other groups.

Q: What prompted this?

A: The number of applications for tax-exempt social welfare organizations doubled from 2010 to 2012, to 3,400 a year. That's largely because of a surge in politically oriented groups before the 2012 presidential election and in the wake of favorable court rulings, the IRS says. In response, an IRS unit in Cincinnati began to sort politically oriented groups into a separate "bucket" of applications. IRS Exempt Organizations Director Lois Lerner said this was done for consistency and is not unlike what the IRS has done with special treatment of other groups that raise new tax law issues, such as credit counseling agencies and non-profit news organizations.

Q: What is the normal process for seeking tax-exempt status?

A: The organization files an application and answers a 36-item questionnaire on its structure, purpose and activities. Based on those answers, the IRS may seek additional information. An organization can skip the recognition step and simply file a tax return.

Q: Is this like an audit?

A: No. The Tea Party groups were seeking tax-exempt status even before filing a tax return. Tax-exempt groups accused of violating tax laws by directly engaging in political campaigns can have their status revoked - but that's a separate process conducted by a different IRS unit in Dallas.

Q: How many Tea Party groups were affected?

A: Lerner said about 300 groups went into a "bucket" of applications getting more scrutiny. About a quarter of them were groups that had "Tea Party" or "Patriot" in their names, she said. The others may have drawn scrutiny based on broader criteria that pulled out groups whose issues involved government spending or debt, or whose goals were critical of the government, according to a timeline provided to members of Congress.

Q: This happened at the IRS office in Cincinnati. Were groups in other parts of the country affected?

A: Yes. The Cincinnati office handles the intake of tax-exempt applications for all organizations in the country.

Q: When did the targeting of Tea Party groups begin? When did it end?

A: According to a timeline compiled by independent IRS investigators, the IRS first began searching for Tea Party-related groups in March 2010. The policy underwent several revisions through 2011 and 2012 and now involves only organizations with "indicators of significant amounts of political campaign intervention."

Q: How were the Tea Party groups harmed?

A: The additional scrutiny held up tax-exempt applications for months, although the IRS says no applications have been denied. Groups caught in this process did not receive IRS documentation, which can provide legitimacy and assist with fundraising. Some conservative groups say their rights to freedom of association were violated through invasive questioning.

Q: How has the IRS attempted to fix the problem?

A: The IRS says it has destroyed any donor lists that were improperly obtained. It says it has begun to clear out the backlog of tax-exempt applications, approving about 130 of the initial 300. About 25 groups have withdrawn their applications.

Q: Who at the IRS was involved?

A: Lerner said Friday it was "low-level" and "front-line" employees who made the initial determination. The timeline shows that Lerner herself was briefed in 2011 and that lawyers and managers from several units were involved. It's unclear when IRS Commissioner Douglas Shulman - appointed by President George W. Bush to a five-year term in 2008 - first learned of the practice. Shulman stepped down in November. The acting commissioner is Steven Miller. Lerner said she never discussed the issue with the Department of the Treasury or the White House. White House spokesman Jay Carney said the White House counsel first learned of the investigation last month, and the president learned Friday.

Q: What happens next?

A: The Treasury Inspector General for Tax Administration says it will release its report on the matter this week. The chairmen of the tax-writing committees in the House and Senate have promised hearings, the first of which will be before the House Ways and Means Committee on Friday.